Although The Glass Menagerie shows more pathos (appeal to the sentiment of the reader) than comedy, one could argue that we could consider as "comedic" any element within the play that helps us see the situation in the Wingfield family form a much lighter perspective.

This being said, we could argue that Amanda Wingfield provides, at specific points in the play, quite the comedic element. One of these instances occurs at the beginning, when she tells her stories about the South, where she would expect gentlemen callers in the afternoons. What is funny about this is that her children, Tom and Laura, seem to be quite used to her telling the same story, with the same upbeat attitude. However, Laura asks Tom to let their mother tell the story; after all, it is the only cheerful tales they really ever listen to in their dreadful city apartment. 

There were the Cutrere brothers, Wesley and Bates. [..] His widow was also well provided for, came into eight or ten thousand acres, that's all. She married him on the rebound - never loved her - carried my picture on him the night he died !And there was that boy that every girl in the Delta had set her cap for! That brilliant, brilliant young Fitzhugh boy from Greene County!

TOM: What did he leave his widow?

AMANDA: He never married ! Gracious, you talk as though all of my old admirers had turned up their toes to the daisies !

TOM: Isn't this the first you've mentioned that still survives ?

Here the comedic element is picturing Tom, above all people, actually following his mother's conversation, because he has heard it already so many times. 

Moreover, when the prospect of Jim O'Connor's visit becomes a reality, we can certainly giggle when we picture Amanda's desperate preparations for the dinner, as well as when we realize that Amanda has donned one of the most ridiculous dresses she could possibly wear in a last attempt to reignite her past as a former Cotillion Belle. This scene is sure to cause a stir in a typical audience. 

AMANDA: Something I've resurrected from that old trunk! Styles haven't changed so terribly much after all.

[She parts the portières.] Now just look at your mother !

[She wears a girlish frock of yellowed voile with a blue silk sash. She carries a bunch of jonquils - the legend of her youth is nearly revived.]

[Feverishly]: This is the dress in which I led the cotillion, won the cakewalk twice at Sunset Hill, wore one spring to the Governor's ball in Jackson ! See how I sashayed around the ballroom, Laura? [She raises her skirt and does a mincing step around the room.] I wore it on Sundays for my gentlemen callers !

Hence, the image of a middle-aged woman with a hyperactive temper and a crazy disposition to remain attached to the past may be a sight too sad for the sensitive eye, but there is certainly an element of comedy that Tennessee Williams may have wanted to include to lighten up an otherwise depressing, but realistic, plot.